1. Field of the Invention
The present invention relates to arc lamps. More specifically, the invention relates to a high pressure neon arc lamp configured to efficiently produce incoherent light having wavelengths between about 625 nanometers and about 645 nanometers.
2. Relevant Technology
Light is a form of electromagnetic energy. Electromagnetic energy is divided into different spectrums based on the wavelength of the electromagnetic energy. Visible light is one of these spectrums. Within the visible light spectrum, light wavelengths may be identified by color. For example, light having wavelengths between about 625 nanometers and 645 nanometers appear to an observer as red. Electromagnetic energy with shorter wavelengths than visible light comprise the ultra-violet (UV) band of the spectrum. Electromagnetic energy with longer wavelengths than visible light comprise the infrared band of the spectrum.
Producing and using visible light is well understood. For example, it is conventional to produce light of different wavelengths using a variety of techniques such as incandescent, fluorescent, and arc lamps. It is also conventional to split or separate the different colors in light using a prism. Light can also be focused and intensified using conventional laser technology.
Visible light serves some important uses. Light is useful for interior and exterior lighting, traffic signals, tanning of skin, as well as a variety of other uses. Additionally, light is useful in medicine. Concentrated coherent light in the form of lasers provides very precise cutting tools for surgeons.
One field of medicine involves the use of light in a way other than as a high precision cutting tool. Photodynarnic therapy (PDT) is a medical treatment that uses visible light to activate a drug designed to destroy particular cells within a patient""s body. PDT is becoming very popular. Generally, PDT involves a two part procedure for treating infectious diseases as well as cancer.
PDT begins by administering to a patient a drug known as a photosensitizer. Photosensitizers are drugs that are specifically engineered to target a particular kind of cell and tissue within the patient. Several photosensitizers are known including proprietary drugs such as Photofrin(copyright). Generally, the photosensitizer is administered by injection. The photosensitizer may enter into, attach to, or surround the targeted cells and/or tissues. By way of example, PDT used to treat cancer involves photosensitizers that enter into the cancerous cells. The administration of the photosensitizer is completely harmless to the patient.
Next, PDT involves illuminating the target tissue, such as cancer cells, with a non-thermal, low powered light. Generally, this light should be red having wavelengths between 625 nanometers and 645 nanometers. Illumination of the target tissue with red light activates the photosensitizer to destroy the target tissue. Conventionally, the light source used is a low power laser.
Light of the red wavelength activates the photosensitizer concentrated in and around the target cells. In cancerous cells, the photosensitizer cooperates with oxygen to create an oxygen free-radical that destroys the cancerous cell. Because the photosensitizer exists primarily in the cancerous cells, the healthy cells remain unharmed. Unlike radiation therapy, PDT may be repeated with little recuperation time required for the patient. PDT may also be used to treat acne, remove unwanted hair, and in other applications. Generally, the effectiveness of PDT treatment depends on the amount of photosensitizer administered and the ability to illuminate enough of the photosensitizer at an appropriate intensity.
Generally, low powered, non-thermal lasers are used to activate the photosensitizer. There are several limitations to using lasers in PDT. Chief among the limitations of low powered, non-thermal lasers is the small area of illumination. Due to the nature of lasers and the manner in which they are generated, a very concentrated and small laser beam is generally created. Consequently, the laser beam has a small illumination area. Techniques exist to diffuse the laser light. However, such diffusion decreases the tissue penetration capability of the laser beam. The laser beam loses intensity. A small illumination area requires that the laser beam make several sweeps of an infected or cancerous area to illuminate the target cells. This increases the time required for treatment and may result in areas of tissue not being illuminated due to human error.
The limitation due to small illumination area is compounded when PDT is used to treat anti-biotic resistant infectious diseases of the skin. These diseases may cover large areas of a patient""s skin. Thus, it is difficult to adequately treat these diseased areas using a laser with a small beam area. Effective treatment of the disease using PDT with lasers may require repeated illumination treatments.
Additionally, lasers are relatively expensive because by definition they produce coherent light. Coherent light is light in which all the photons are in phase. The cost is also high due to high power requirements for lasers. The expense used to produce coherent laser light is largely wasted when used for PDT.
PDT requires only a particular wavelength of photons to function. Coherency of the light is not a requirement. The photosensitizer is activated by the wavelength of the light. Generally, photosensitizers are activated regardless of the coherency of the light.
Additionally, lasers are generally very large and bulky in comparison to other medical equipment. Often, the portability of these devices is limited. Generally, the patient must be brought to the laser rather than the laser to the patient. Lasers may also require specialized training to operate.
PDT may also be used with incoherent light sources such as high pressure xenon or krypton arc lamps. A high pressure arc lamp is a lamp that creates light by passing an electrical arc between two electrodes through a specific gas. With high pressure xenon and krypton arc lamps the gas between the electrodes is pressurized to several hundred Torr. The gas is also substantially pure xenon or krypton. Generally, a xenon and krypton arc lamp provides a greater illumination area because the light is diffuse.
Xenon and krypton arc lamps however do not efficiently produce high intensity red light having wavelengths between 625 nanometers and 645 nanometers. The light generated by xenon and krypton arc lamps has wavelengths ranging from red to ultraviolet (UV). The majority of the light photons generated by xenon and krypton arc lamps are in the UV band of the electromagnetic spectrum. To provide the red light needed for PDT, the UV light is filtered out from the xenon and krypton arc lamp""s output. UV light is also filtered to avoid burning the tissue of the patient. Because a majority of the light produced by a xenon or krypton arc lamp is filtered, the lamps are generally very inefficient.
Accordingly, what is needed is a high pressure arc lamp that efficiently produces photons in the red band of the electromagnetic spectrum, light having wavelengths between 625 nanometers and 645 nanometers, with minimal power requirements. Additionally, what is needed is a high pressure neon arc lamp that is less expensive to fabricate than conventional laser devices. Further, what is needed is a high pressure neon arc lamp that provides a comparably large illumination area at an operable intensity when compared to convention red light sources such as lasers. Such an invention is disclosed and claimed herein.
The invention is a high pressure neon arc lamp and method for using the lamp in photodynamic therapy. Conventionally, lasers, and xenon or krypton arc lamps are used in photodynamic therapy to provide a red light to activate photosensitive drugs within a patient to kill cells of cancer or other infectious diseases. However, xenon and krypton arc lamps produce mostly ultra-violet light rather than red light. Lasers can produce red light but are expensive and generally illuminate only a small area of tissue. The small illumination area of lasers may require multiple laser treatments to activate all the photosensitive drug in the patient. The present invention resolves these problems by producing mostly red light and illuminating a larger area than most lasers.
The high pressure neon arc lamp is a light source that may be configured to use a conventional electrical wall outlet. The high pressure neon arc lamp produces more red light at a higher intensity than xenon or krypton arc lamps. The high pressure neon arc lamp may also be smaller and cheaper to produce than conventional red lasers.
The high pressure neon arc lamp includes a sealed housing. Preferably, the sealed housing is translucent and configured to seal a quantity of substantially pure neon gas inside. Neon gas is used because its spectral signature is mostly light of red wavelengths. The spectral signature is a unique set of light wavelengths emitted when an atom of a particular element gains or loses energy.
The neon is preferably pressurized to between about 500 and about 22,000 Torr. The housing includes a bore that preferably extends coaxially within the housing. The pressurized neon gas is stored within the bore. The bore allows an electrical arc emitting red light to travel through the neon.
Preferably, the sealed housing is cylindrical. A cylindrical housing is inexpensive to fabricate and allows for a large electrical arc to pass through the bore. The longer the electrical arc, the larger the area that is illuminated by the lamp. A cylindrical shape also provides an effective container for neon gas at the pressures mentioned above. In a preferred embodiment, the diameter of the bore is consistent along the bore""s entire length.
The sealed housing includes a first electrode and a second electrode installed on each end. The first electrode and second electrode provide an electrical path between an area outside the housing and the bore within the housing. The first electrode and second electrode are configured to facilitate passing of an electrical arc through neon gas within the bore.
The sealed housing is electrically coupled by the first electrode and second electrode to a voltage source. Preferably, the voltage source is a pulse generator configured to deliver a voltage in the range of 24 kilovolts to 30 kilovolts between the first electrode and the second electrode. Alternatively, the voltage source may supply a constant voltage between the first electrode and the second electrode. One voltage source provides a voltage pulse to overcome electrical impedance of the neon gas of the bore and a subsequent voltage source passes an electrical arc between the first electrode and the second electrode.
The pulse generator may be configured to provide a pulse of voltage at a rate influenced by the average power desired. The higher the average power, the higher the pulse repetition rate. The voltage pulse rate provides a sensitive technique for adjusting the average light power. Each pulse of voltage preferably creates an electrical arc between the first electrode and the second electrode. The electrical arc produces photons having wavelengths between about 575 nanometers and about 695 nanometers.
The present invention includes a method of using the high pressure neon arc lamp as a photosensitive drug activation device. Photosensitive drugs (also known as photosensitizers) are drugs which are activated by light, particularly light of specific wavelengths. The effect of activation of the drug depends largely on how the drug is engineered.
For example, photosensitive drugs used to treat cancer are designed to enter into the cancerous cells of a patient prior to activation of the drug. Photosensitive drugs used to treat cancer are generally activated using light having red wavelengths. The light interacts with the drug to generate an oxygen free radical. The oxygen free radical is created within the cancer cell. The membrane of the cancer cell is ruptured by the oxygen free radical. Thus, the cancer cell is destroyed.
According to a first step of the method, a photosensitive drug is administered to a patient. Generally administration of the drug is done intravenously to allow the drug to quickly attach to, enter, or surround target cells within the patient. The target cells are those that are unwanted.
Next, the photosensitive drug is allowed to be absorbed by target tissue such as cancer cells within the patient. The time for absorption may be a few hours to as long as a day or two. As the drug begins the be absorbed the patient must avoid premature exposure to light of red wavelengths. Premature exposure may activate the drug before it has singled out the target tissue. Generally, the patient must stay in-doors away from sunlight.
Then, target tissue is illuminated by the high pressure neon arc lamp to activate the photosensitizer drug and destroy the target cells. The high pressure neon arc lamp may be brought to the patient. The high pressure neon arc lamp illuminates such as large area that a single pass of the light may be all that is necessary. Additionally, because the procedure is non-invasive the patient may return to normal activities the same day.
These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.